Ad-Hoc recovery in workflows, a formal model and some system support aspects

How to increase flexibility has always been an issue relating to the applicability of any workflow system. We address this issue in one case where an agent needs to alter the control flow prescribed in the original definition to some previous executions. This phenomenon is termed ad-hoc recovery. Ad-hoc recovery is usually caused by unpredictable reasons, such as unexpected output Of some individual tasks, events or exceptions due to the changing environment. Due to its irregularity in nature, ad-hoc recovery in general cannot be dealt with by approaches to handling failure recoveries. On the other hand, since it allows normal control flows to be diverged from at run time without modifying workflow schema, it enjoys higher flexibility than the fixed schema systems while pays a lower cost than schema evolution. In this paper, we introduce the concept of ad-hoc recovery, and characterize its main features. We also discuss some implementation issues